A thermoplastic resin is molded, from its excellent moldability and processability by various processing methods, for example, injection molding, blow molding, sheet molding, film molding, extrusion molding, press molding, etc., and is used to produce products for uses in a wide range such as electric/electronic equipment, OA (office automation) equipment, equipment for vehicles, miscellaneous goods, etc. In particular, injection molding becomes a main processing method for a thermoplastic resin in terms of a high productivity and a high shape freedom.
Further, in the case where particularly high strength, stiffness and thermal resistance is required for a thermoplastic resin, a method of modifying the raw material by adding fibrous filler is generally employed. As a typical example of such a raw material, exemplified are fiber reinforced thermoplastic resin pellets obtained by melt kneading a thermoplastic resin and glass fibers or carbon fibers together by an extruder when the thermoplastic resin is pelletized. However, if injection molding is carried out using the fiber reinforced thermoplastic resin pellets thus obtained, because the fibrous filler is oriented in a core layer in a direction perpendicular to a resin flow direction at the time of injection molding and oriented in a skin layer in the resin flow direction, anisotropy is generated in strength and shrinkage. As a result, with respect to a molded body obtained, warping increases.
As a means of solving such a defect, long fiber pellets for the purpose of strengthening and reducing the warping by lengthening fibers remaining in the molded body has been developed. However, even if the long fiber pellets are used, when a usual injection molding is carried out, because the orientation directions of fibrous filler are different between in the skin layer and in the core layer, there is still a situation where a satisfactory advantage cannot be obtained.
As a molding method to prevent warping, JP-A-2000-061969 and JP-A-2006-272849 describe an injection press molding method, but there is no description therein as to a method of controlling orientation of fibers in a molded product. Further, with respect to a method of reducing warping in a molded body, JP-A-2003-171564 describes an effect of reducing warping by giving a characteristic to a resin to be combined, but it does not control warping from anisotropy of fiber orientation. Further, as a means of disturbing orientation of fibers in a molded body, JP-A-2002-166452 describes a structure of a mold having a movable insert die. In that mold, orientation of fibers is disturbed by rotating the cavity surface to give a shear to a material to be molded into a molded body, but the ability to disturb the orientation is small, and there is a limitation in shape of the molded body. Furthermore, JP-A-2002-096356 describes a molding device with a mold for injection press molding which has a structure of a waste cavity (dummy cavity), but it does not describe as to molding of a fiber reinforced resin at all.
It could therefore be helpful to provide an injection molded body which is excellent in strength and stiffness, small in anisotropy of strength in the molded body and extremely low in warping, and a method of producing the same.